Method of manufacturing a vessel for storage of pressurized fluid

Abstract

The invention relates to a method of manufacturing a vessel (21) suitable for storage of pressurized fluid. The method comprises providing a body (22) forming an inner vessel cavity, the body having an inlet (25) providing an opening into the inner vessel cavity, providing at least one reinforcing element (1) and arranging it aligned with the inlet, winding continuous fibre reinforcement (24) around the body to form the vessel, and solidifying the matrix material impregnating the fibres. The at least one reinforcing element comprises a circumferential member (2) with a through-going hole (9), and a plurality of element fibres (3) extending away from the circumferential member while being in engagement with the circumferential member. During the winding, it is ensured that the element fibres are arranged in an overlapping and / or sandwiching engagement with the continuous fibre reinforcement over a region around the inlet.

Description

[0001] METHOD OF MANUFACTURING A VESSEL FOR STORAGE OF PRESSURIZED FLUID

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method of manufacturing a vessel for storage of pressurized fluid. In particular, it relates to such a method comprising winding of continuous fibres and wherein the vessel comprises a reinforcing element arranged at an inlet into an inner vessel cavity in order to provide reinforcement thereof.

[0004] BACKGROUND OF THE INVENTION

[0005] The present invention has been developed within the field of high-pressure vessels for hydrogen storage, but it can be used within any type of vessel where it is relevant to limit the stresses and deformations around an inlet or outlet. High- pressure vessels play a crucial role in the green transition across various sectors, including automotive, primarily trucks for road transportation, energy storage solutions, aviation, and space vessels.

[0006] A vessel of the type relevant for the present invention typically consists of three types of primary components: an inner liner serving as a diffusion barrier, a boss positioned at each end of the pressure vessel, and a layer of carbon or glass fibres which have been applied by winding. The boss, situated at both ends, presents a weak point in a high-pressure vessel due to the majority of fibres being oriented perpendicular to the loading direction in that area, and this results in considerable stresses and deformations. In the worst case, such stresses and deformations may cause leakage of the fluid stored in the vessel. To address this issue, large and complex bosses are typically employed, which not only incur significant costs but also contribute to 20-30% of the total weight of the pressure vessel, the numbers varying depending on its size and intended application.

[0007] OBJECT OF THE INVENTION

[0008] It is an object of the present invention to provide a method of manufacturing a vessel suitable for storage of pressurized fluid by which the stresses and deformations around the inlet into an inner cavity of the vessel can be lower than with known vessels.

[0009] It is another object of the present invention to provide such a method with which the weight of the vessel can be lowered without compromising the load bearing capacity of the material around the inlet.

[0010] In is an object of at least some embodiments of the present invention to provide such a method with which a vessel without a traditional boss can be made.

[0011] It is another object of at least some embodiments of the present invention to provide a method of manufacturing a vessel with which a lower risk of leakage can be obtained.

[0012] It is a further object of the present invention to provide an alternative to the prior art.

[0013] SUMMARY OF THE INVENTION

[0014] The above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a method of manufacturing a vessel suitable for storage of pressurized fluid, the method comprising the steps of:

[0015] - providing a body forming an inner vessel cavity, the body having an inlet providing an opening into the inner vessel cavity,

[0016] - providing at least one reinforcing element comprising:

[0017] - a circumferential member with a through-going hole, and

[0018] - a plurality of element fibres extending away from the circumferential member while being in engagement with the circumferential member,

[0019] - arranging the at least one reinforcing element with the hole being aligned with the inlet,

[0020] - winding continuous fibre reinforcement around the body to form the vessel while ensuring that the element fibres are arranged in an overlapping and / or sandwiching engagement with the continuous fibre reinforcement over a region around the inlet, and if the fibres are dry, impregnating them with matrix material and solidifying the matrix material, or if the fibres are pre-impregnated with matrix, solidifying the matrix material.

[0021] "Fluid" may be liquid or gas. The vessel may be for storage of e.g. N2, H2, Ar, or He. It may also be for storage of e.g. one of the following fluids which are liquid at certain pressures above atmospheric pressure: N2O, Propane, Ethane, CO2, and Coolants like LMP-103S.

[0022] In the description of the invention, reference will be made to inlet only. However, the vessel may also be provided with an outlet at the opposite end, and this outlet may be made in the same way as the inlet.

[0023] The word "element" in relation to "element fibres" is used because these fibres are related to the reinforcing element and to distinguish them from the continuous fibres forming part of the surrounding composite material.

[0024] By "in engagement with", in relation to the mutual arrangement of the element fibres and the circumferential member, is preferably meant that a force applied to the circumferential member can be transferred to the element fibres due to the engagement. The element fibres can e.g. be arranged within the hole in the circumferential member so that in the manufactured vessel, the element fibres are arranged through the hole in the circumferential member while having the element fibres extending away from the hole in the circumferential member; examples will be shown in the figures. However, the element fibres may also be arranged in further holes or slits provided in the circumferential member.

[0025] The wording that the element fibres are arranged in an overlapping engagement with the continuous fibre reinforcement also covers the embodiments to be described below in which the element fibres are integrated into the liner. Thus, the "overlapping" does not necessarily mean in direct contact.

[0026] By incorporating at least one reinforcing element into a vessel, it is possible to arrange the element fibres in the orientations where large stresses occur around the inlet in a vessel storing pressurized fluid. This will add strength in other orientations than those of the continuous fibres arranged by winding whereby the stresses and deformations around the inlet can be distributed over a larger area so that the maximum values reached are lowered. At least for some application, this may make it possible to replace carbon fibre reinforcement with glass fibre reinforcement which is significantly cheaper. Alternatively or in combination therewith, it may also be possible to meet the requirements for a given application with less material which will influence both weight and cost.

[0027] In some embodiments of the invention, the body is a liner configured to remain in the vessel and delimit the inner vessel cavity. Hereby the liner forms a coherent body of which the fluid-tightness can be tested before the subsequent winding. Such embodiments were analysed during the development of the invention and will therefore be illustrated in the figures. The liner may be made from a material with specific chemical resistance chosen depending on the intended use of the vessel.

[0028] Such a fluid-tight liner may be made by casting, and in such embodiments the element fibres of at least one of the at least one reinforcing element may be integrated into the liner during the casting. This may be obtained by arranging the respective at least one element in the mould or tool in which the liner is cast, before the liner material is filled into the mould or tool. In such embodiments, the inlet may be provided as a traditionally used boss, or it may be provided without the need for such a boss as will be described in the following. There may additionally be at least one reinforcing element arranged outside the liner.

[0029] In alternative embodiment to those comprising a liner, the body may be a flexible bladder configured to be inflated before the step of winding and to be deflated and removed from the vessel after the matrix material has solidified. Hereby it may be possible to lower the weight of the vessel which is of particular importance within aviation and space related applications. It may also be possible to lower the cost. For embodiments made with a flexible bladder, it will typically be necessary to apply a coating to the inner surface of the vessel cavity to ensure that it is fluid- tight. In any of the embodiments described above, the element fibres may be provided in a configuration selected from bundle, band, and / or stretchable sleeve. When they are provided as bundles or bands, these may be arranged at different parts of the circumferential member so that they extend in different directions. Preferably they are evenly distributed around the circumferential member to take up forces from the pressure in the vessel due to the pressurized fluid. The element fibres may also be provided as two or more stretchable sleeves arranged inside each other as will be shown in the figures. A stretchable sleeve typically comprises fibres that are connected, such as interwoven, in a loose and thereby stretchable tubular configuration. The connection, such as interweaving, provides some mutual support to the fibres whereby it may be easier to arrange and keep them in the desired positions until they are fixated by the solidified matrix. A further advantage of a sleeve is that it can hereby be easier to ensure an even distribution of the element fibres, so that the forces caused by the pressure inside the vessel can be distributed into a region around the hole.

[0030] In some embodiments of the invention, the circumferential member is a solid ring. Alternatively, the circumferential member can e.g. be continuous fibres wound around the element fibres. A solid ring is found suitable for ensuring an even distribution of the forces applied during use. Furthermore, a metal ring can be used to improve the fatigue strength, if it is made in a material with sufficiently high fracture toughness to suppress any fatigue crack growth. The fatigue properties may be further improved by using a solid ring with low surface roughness.

[0031] The reinforcing element may further be provided with a circumferential insert having an outer surface configured for supporting the circumferential member. The outer surface of the circumferential insert may e.g. have a recess adapted to receive and hold the circumferential member in place. Hereby it will be easier to keep the different parts aligned in the correct mutual positions during the manufacturing process. An example of a possible design will be shown in the figures.

[0032] In embodiments comprising a circumferential insert, the circumferential insert may form the inlet by having an inner surface forming the opening of the inlet. Thereby the circumferential insert can replace the traditionally used boss, and the reinforcing element can be used to distribute the forces over a large part of the vessel. Computer simulations made during the development of the present invention have shown that hereby the dimensions of such a circumferential insert can be significantly smaller than those of a traditionally used boss without compromising the load transferring properties. A large amount of the total weight of a traditionally made vessel is due to the boss arranged at both ends. Thus, by at least some embodiments of the present invention, the weight can be lowered which at least for some applications will be an important advantage.

[0033] Alternatively, the inlet may be a separate component not forming part of the reinforcing element. Such a separate component may e.g. resemble a traditionally used boss. Typically smaller dimensions thereof may be sufficient because of the load transferring effect of the element fibres as described above.

[0034] In embodiments in which the at least one reinforcing element comprises a circumferential insert, the outer surface of the circumferential insert has a recess adapted to receive and hold the circumferential member in place.

[0035] In embodiments in which the body is a fluid-tight liner and in which the at least one reinforcing element comprises a circumferential insert, the circumferential insert may have an outwardly extending flange engaged with a mating groove in the liner thereby preventing axial movement of the circumferential insert relative to the liner.

[0036] In alternative embodiments in which the body is a fluid-tight liner, the method may further comprise the steps of:

[0037] - providing an inner ring having an outwardly extending flange engaged with a mating groove in the liner thereby preventing axial movement of the inner ring relative to the liner, and

[0038] - arranging the at least one reinforcing element around the inner ring.

[0039] With such embodiments, the inner ring can replace the traditionally used boss, and thereby provide some of the same advantages as described above. In embodiments in which the at least one reinforcing element comprises a circumferential insert, the circumferential insert may be made from a material selected from : metal, polymer, ceramic and composite. Which material to use for a given application will typically be determined from the intended use of the vessel both with respect to stored fluid and the surroundings, such as pressure and temperature.

[0040] In some embodiments of the invention, a plurality of reinforcing elements arranged in series is used. Such embodiments may be particularly useful for vessels having large wall thickness so that the stresses around the inlet can be distributed over a larger volume.

[0041] In embodiments comprising more than one reinforcing element, these reinforcing elements may be of the same type or different. As an example, embodiments in which the element fibres of at least one reinforcing element are integrated into the liner may comprise a differently designed reinforcing element integrated with the continuous fibre reinforcement.

[0042] In a second aspect, the invention relates to a vessel suitable for storage of pressurized fluid, the vessel being manufactured by a method according to any of the embodiments of the first aspect of the invention.

[0043] The first and second aspects of the present invention may be combined so that all the features mentioned in relation to the first aspect of the invention also apply to the second aspect of the invention. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0044] BRIEF DESCRIPTION OF THE FIGURES

[0045] The method of manufacturing a vessel according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. Figure 1 is a photo of a prior art vessel.

[0046] Figure 2 is a flow-chart showing the overall steps of a method according to the invention.

[0047] Figures 3A-3D schematically show different examples of a reinforcing element.

[0048] Figure 4 schematically shows a three-dimensional cross-sectional view through a circumferential insert.

[0049] Figure 5 schematically shows a cross-sectional view of an example of a reinforcing element.

[0050] Figure 6 schematically shows how a reinforcing element with element fibres in the form of a stretchable sleeve can be arranged.

[0051] Figure 7A shows a side view and an end view of a conventional liner with a boss. Figure 7B shows an end view of a similar liner wherein the element fibres of a reinforcing element are integrated into the liner during the casting.

[0052] Figures 8A and 8B schematically show cross-sectional views of an embodiment of the invention in which the boss is configured to position a reinforcing element integrated in the liner.

[0053] Figures 9A, 9B, and 9C show a Finite Element model which has been used for analysis during the development of the present invention.

[0054] Figures 10A to 10D schematically show possible additional features that may be added to the design of the boss in order to prevent slip during the winding of the continuous fibre reinforcement around the liner. DETAILED DESCRIPTION OF AN EMBODIMENT

[0055] Figure 1 is a photo of a prior art vessel 21 suitable for storage of pressurized fluid, such as hydrogen or one of the other fluids mentioned above. It comprises three types of primary components: an inner liner 22 serving as a diffusion barrier, a boss 23 positioned at each end of the pressure vessel, and a layer of composite material with wound continuous fibres 24. To the right in the figure is a liner 22 with the boss 23 seen at one end, and to the left is a vessel 21 comprising the outer layer of wound carbon fibres 24.

[0056] A method of manufacturing a vessel 21 suitable for storage of pressurized fluid will be described in the following with reference to embodiments comprising providing a body forming an inner vessel cavity, the body having an inlet 25 providing an opening into the inner vessel cavity. Such a body will typically be a fluid-tight liner 22 configured to remain in the vessel 21 and delimit the inner vessel cavity, the liner resembling the one shown in figure 1. However, as described above, the body may alternatively be a flexible bladder configured to be inflated before the step of winding and to be deflated and removed from the vessel after the matrix material has solidified.

[0057] Figure 2 is a flow-chart showing a method according to the invention. The method comprises the following overall steps which will be described in more details below:

[0058] A: Providing a body 22 with an inlet 25, the body forming an inner vessel cavity.

[0059] B. Providing at least one reinforcing element 1 at the inlet.

[0060] C. Winding continuous fibre reinforcement 24 around the body 22 to form the vessel 21.

[0061] DI: If the fibres are dry, impregnating them with matrix material and solidifying the matrix material, or

[0062] D2: If the fibres are pre-impregnated with matrix, solidifying the matrix material.

[0063] Figures 3A-3D schematically show different examples of a reinforcing element 1. It comprises a circumferential member 2 with a through-going hole 9, and a plurality of element fibres 3 extending away from the circumferential member 2 while being in engagement with the circumferential member 2. Step B in figure 2 comprises arranging the at least one reinforcing element 1 with the hole 9 being aligned with the inlet 25 of the body 22. Step C in figure 2 comprises ensuring that the element fibres 3 are arranged in an overlapping and / or sandwiching engagement with the continuous fibre reinforcement 24 over a region around the inlet. In the examples shown in figures 3A-3D, the circumferential member 2 is provided in the form of a solid ring which may e.g. be made from metal, polymer, ceramic, or composite material. Figure 3A shows the element fibres 3 in the form of bundles 3a of fibres arranged evenly with respect to the circumferential member 2. Figure 3B shows the element fibres in the form of bands 3b of element fibres, and figure 3C shows the element fibres in the form of a stretchable sleeve 3c. Such a stretchable sleeve 3c is typically provided as woven fibres in a tubular configuration and should be loose enough to allow for the two parts thereof being stretchable into a configuration of use, wherein they typically extend radially away from the circumferential member 2. In the figures, the element fibres are shown as extending parallel to each other before being spread out for ease of illustration only. In practise, they will typically be interwoven or held together by stitching. It will also be possible to use two or more sleeves 3c arranged inside each other as shown schematically in figure 3D.

[0064] As described above, the reinforcing element 1 may be provided with a circumferential insert 4, and an example thereof is shown in figure 4 which is a three-dimensional cross-sectional view through the circumferential insert 4. It has an outer surface 6 configured for supporting the circumferential member 2. In the illustrated embodiment, the outer surface 6 of the circumferential insert 4 has a recess adapted to receive and hold the circumferential member 2 in place. An example of such an embodiment is shown schematically in figure 5 in which the element fibres are shown in the form of a stretchable sleeve 3c which has been stretched into a configuration where the two halves overlap. This arrangement can e.g. be obtained as shown in figure 6 where a guide mandrel 11 is used for holding the different parts in place during the arrangements thereof. In the embodiment in figure 6, the circumferential member 2 is in the form of wound fibres instead of a solid ring. In some embodiments of the invention, the circumferential insert forms the inlet into the inner vessel cavity by having an inner surface 5 forming the opening of the inlet. Figure 7A shows a side view and an end view of a conventional liner 22 with a boss 23. Such a liner is typically made by casting. Figure 7B shows an end view of a similar liner 22 wherein the element fibres 3a of a reinforcing element 1, seen as black lines in the figure, are integrated into the liner during the casting.

[0065] Figures 8A and 8B schematically show cross-sectional views of an embodiment of the invention in which the boss 23 is configured to position a reinforcing element 1 which is to be integrated in the liner 22. Figure 8A shows the boss 23 having a geometry which is configured to hold a reinforcing element 1 in place. The reinforcing element 1 comprises a circumferential member 2 in the form of a ring and element fibres in the form of a sleeve 3c. These element fibres 3c are preferably pre-impregnated with the same material as the liner 2. The boss 23 with the reinforcing element 1 is inserted in the mould or tool used for the casting of the liner 22 so that the element fibres 3c become integrated with the liner 22 during the casting. The element fibres 3c may be pre-melted onto a foil (not shown) to ease the arrangement of the element fibres 3c in the mould or tool. Figure 8B schematically shows a further reinforcing element 1, illustrated as corresponding to the one in figure 5, arranged on top of the reinforcing element 1 that is cast into the liner 22. The element fibres 3, which may also be in the form of a sleeve 3c, of this upper reinforcing element 1 is integrated into the continuous fibre reinforcement 24 during the winding process as described above. The upper reinforcing element 1 in figures 8A and 8B comprises a circumferential insert 4 with an inner surface 5 configured to engage with an outer surface of the boss 23. An advantage of using a boss 23 as shown in figures 8A and 8B in combination with reinforcing elements 1 as shown, is that the weight of the boss 23 can be lower than for a traditionally used boss 23. The design of the boss 23 can also be simpler than for a traditionally used boss whereby the manufacturing cost can be lower. Furthermore, the smaller amount of metal means that less heat conduction which may be advantageous when the vessel 21 is used for storage of e.g. liquid N2, H2, or He.

[0066] The development work leading to the present invention has included Finite Element analysis which showed that with a vessel manufactured with a method according to the present invention, the stress level around the inlet can be significantly lowered compared to a corresponding prior art solution. Figure 9A shows a cross-sectional view of the model used in this analysis, and figure 9B shows a partial view of the same model at the region around the inlet. As seen from figure 9B, the model included two reinforcing elements arranged in series. As also seen from figure 9B, the model has been made on an embodiment of the invention comprising an inner ring 26 which has an outwardly extending flange 27 engaged with a mating groove 28 in the liner 22. Such a design prevents axial movement of the inner ring, and thereby the reinforcing element 1 arranged around it, relative to the liner 22. Figure 9C shows the same model as in figure 9B but without the wound continuous fibres to illustrate the two reinforcing elements 1 more clearly.

[0067] During the winding process used for the application of the continuous fibre reinforcement 24, the boss 23 is responsible for transferring the torque corresponding to the fibre tension. With a method according to at least some embodiments of the present invention, the flange area 29 of the boss 23 is significantly reduced, and it may be advantageous is to prevent slip between the liner 22 and boss 23 by introducing geometric features to the flange. Figures 10A to 10D schematically illustrate possible additional features that may be added to the design of the boss 23 in order to prevent slip during the winding of the continuous fibre reinforcement 24 around the liner 22. Figure 10A is a cross- sectional view through a boss 23 with a flange 29 which is smooth and circular. Figure 10B is a top view of a boss 23 with rounded cut-outs 30 along the circumference. Figure 10C is a top view of a boss 23 with a polygonal flange edge 31. Figure 10D is a side view of a boss 23 having grooves 32 provided in the flange. All these features are considered as effective way of preventing, or at least counteracting, slip between the boss 23 and the liner 22.

[0068] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAIMS1. Method of manufacturing a vessel (21) suitable for storage of pressurized fluid, the method comprising the steps of:- providing a body (22) forming an inner vessel cavity, the body (22) having an inlet (25) providing an opening into the inner vessel cavity,- providing at least one reinforcing element (1) comprising:- a circumferential member (2) with a through-going hole (9), and- a plurality of element fibres (3) extending away from the circumferential member (2) while being in engagement with the circumferential member (2),- arranging the at least one reinforcing element (1) with the hole (9) being aligned with the inlet (25),- winding continuous fibre reinforcement (24) around the body (22) to form the vessel (21) while ensuring that the element fibres (3) are arranged in an overlapping and / or sandwiching engagement with the continuous fibre reinforcement (24) over a region around the inlet (25), and if the fibres (3,24) are dry, impregnating them with matrix material and solidifying the matrix material, or if the fibres (3,24) are pre-impregnated with matrix, solidifying the matrix material.

2. Method according to claim 1, wherein the body (22) is a fluid-tight liner (22) configured to remain in the vessel (1) and delimit the inner vessel cavity.

3. Method according to claim 2, wherein the liner (22) is made by casting, and wherein the element fibres (3) of at least one of the at least one reinforcing element (1) are integrated into the liner (22) during the casting.

4. Method according to claim 1, wherein the body (22) is a flexible bladder configured to be inflated before the step of winding and to be deflated and removed from the vessel (21) after the matrix material has solidified.

5. Method according to any of the preceding claims, wherein the element fibres (3) are provided in a configuration selected from bundle (3a), band (3b), and / or stretchable sleeve (3c).

6. Method according to any of the preceding claims, wherein the circumferential member (2) is a solid ring.

7. Method according to any of the preceding claims, wherein the reinforcing element (1) is further provided with a circumferential insert (4) having an outer surface (6) configured for supporting the circumferential member (2).

8. Method according to claim 7, wherein the circumferential insert (4) forms the inlet (25) by having an inner surface (5) forming the opening of the inlet.

9. Method according to any of claims 1 to 7, wherein the inlet (25) is a separate component not forming part of the reinforcing element (1).

10. Method according to any of claims 7-9, wherein the outer surface (6) of the circumferential insert (4) has a recess adapted to receive and hold the circumferential member (2) in place.

11. Method according to any of claims 7-10 when dependent on claim 2, wherein the circumferential insert (4) has an outwardly extending flange (27) engaged with a mating groove (28) in the liner (22) thereby preventing axial movement of the circumferential insert (4) relative to the liner (22).

12. Method according to claim 2 or any of claims 3-10 when dependent on claim2, the method further comprising the steps of:- providing an inner ring (26) having an outwardly extending flange (27) engaged with a mating groove (28) in the liner (22) thereby preventing axial movement of the inner ring (26) relative to the liner (22), and- arranging the at least one reinforcing element (1) around the inner ring (26).

13. Method according to any of claims 7-12, wherein the circumferential insert (4) is made from a material selected from: metal, polymer, ceramic and composite.

14. Method according to any of the preceding claims, wherein a plurality of reinforcing elements (1) arranged in series is used.

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